This invention relates to kinescope blanking pulse generators which produce blanking pulses which are delayed with respect to a synchronizing pulse initiating the retrace cycle and which are useful in television display arrangements.
A switched synchronous vertical deflection (SSVD) circuit is described in U.S. patent application Ser. No. 595,809, filed July 14, 1975 for Peter Eduard Haferl and entitled "SWITCHED VERTICAL DEFLECTION SYSTEM", in which energy is supplied to the vertical deflection winding on a kinescope by means of switched reactances coupled to the horizontal deflection generator. These switched reactances are controlled by a vertical sawtooth generator, the trace and retrace intervals of which are in turn controlled by the vertical synchronizing signals. A pulse-position modulator driven by the sawtooth generator and synchronized with the horizontal retrace pulses generates switch gating signals which control the switched reactances in a manner to generate a sawtooth deflection current at the vertical rate in the vertical deflection winding. This arrangement has low power consumption by comparison with other vertical deflection circuits and is considered commercially advantageous.
As is well known, it is very advantageous from the point of view of cost and reliability to include as many of the functions of a television receiver as is possible within integrated circuits. Since the low-power portions of a television receiver including a synchronous switched vertical deflection circuit according to the aforementioned U.S. patent application Ser. No. 595,809 are relatively complex, an advantage in cost and reliability, as well as in serviceability, may be obtained by forming the pulse position modulator on an integrated circuit together with other ancilliary circuits such as a blanking pulse generator. It has been discovered, however, that a switched synchronous vertical deflection system according to the aforementioned U.S. patent application Ser. No. 595,809 has an inherent delay between the generated vertical sawtooth and the resulting vertical deflection current which depends upon the design of the deflection winding, which in turn depends upon the kinescope size and type. The magnitude of this delay has been observed to be in the range between 30 and 150 microseconds, and in special cases almost zero. The variation of the delay from receiver to receiver within each type, however, remains relatively constant. Consequently, in order to make it possible for a single control circuit to be used for a large variety of television yoke designs or kinescope sizes, means must be provided for delaying the generation of the kinescope blanking pulse relative to the synchronizing pulse. The delay must be by an amount depending upon the delay of the vertical deflection circuit.
It is known from U.S. Pat. No. 3,931,545, issued on Jan. 6, 1976 to Francis C. Marino to allow the horizontal blanking interval to commence in coincidence with the horizontal synchronizing pulse but to delay the cutoff of the horizontal output transistor by a period of time equal to the entire horizontal sweep period less the transistor storage time by the use of multivibrators coupled in tandem. This, however, is vulnerable to display distortion due to sweep jitter, resulting from the regenerative nature of the multivibrators. Furthermore, the use of tandem coupled multivibrators requires the use of multiple timing capacitors not coupled to the same node, which requires additional interface pins between the external circuit and the monolithic integrated control circuit. Thus, it is desirable to control the delay of the synchronizing pulse with a single externally accessible delay control element.